Symposium FK
Thermoelectrics: Materials Research and Application Technologies


FK-1:IL01  Synergy between Theory, Calculations, and Experiments: How to Improve it
M. FORNARI, Department of Physics and Science of Advanced Materials Program, Central Michigan University, Mt. Pleasant, MI, USA

Recent progress in thermoelectric materials has been built on the synergy between synthesis, characterization, theoretical models, and first principles calculations. Such a synergy, however, is not fully exploited due to misalignments between theoretical concept and standard computational approaches. Using complex minerals as examples, this presentation points to few issues that are crucial to flatten the communication barrier between theory and experiments. The talk will stress the concept of properties descriptors to link computable quantities with functionalities of interest aiming to provide a structure to our intuition. I will also illustrate methodological advances and software innovations which may ultimately aid scientists to unveil hidden relationships in the thermoelectric conundrum.

FK-1:IL02  Assessing the Effect of Synthetic Conditions on PEDOT Thermoelectric Properties: A Combination of First Principles and Classical Molecular Dynamics Simulations
A. Cappai, C. Melis, Department of Physics, University of Cagliari, Cittadella Universitaria, Monserrato (CA), Italy; D. Narducci, Department of Materials Science, University of Milano-Bicocca, Milano, Italy

Organic semiconductors are promising candidates as thermoelectric materials due to their low thermal conductivity and low cost. It is however recognized that the ultimate performances are strongly dependent on the morphological aspects and consequently on the synthesis procedure. In this scenario atomistic simulations provide a fundamental tool to get insights into this problem by obtaining a microscopic description of the polymerization process which is presently not experimentally available. In this work, we present a novel computational tool to model polymerization by means of a suitable combination of first principles DFT simulations and classical molecular dynamics. The present tool allows to generate "in silico" realistic polymer samples starting from the basic monomers by simulating the actual experimental synthesis. The thermoelectric properties of the generated samples are then fully characterized by means of non-equilibrium molecular dynamycs and Marcus theory calcularions. We applied the present procedure to the case of PEDOT-Tos under several experimental conditions i.e. different solvents, oxidants, and temperatures. The overall effect on the morphological and thermoelectric properties will be discussed.

FK-1:IL03  Ab Initio Calculations of Thermal Transport Properties in Semiconductors and Metals
L. CHAPUT, Institut Universitaire de France, Paris Cedex, Université de Lorraine, LEMTA, UMR 7563, Vandœuvre-lès-Nancy, France

During the last 10 years enormous progress has been made for the ab initio calculation of the lattice thermal conductivity of semiconductors. Nowadays, the computations of the anharmonic force constants, and the solution of the Boltzmann equation giving the lattice thermal conductivity are still computationally expensive, but the methodology is well established. Much less work has been done for the ab initio calculation of the electronic part of the thermal conductivity, in doped semiconductors or metals, or for the computation of electrical conductivity and Seebeck coefficient, whose evaluation often relies on the constant relaxation time approximation. In this work, we present an efficient implementation of the electron-phonon interactions, within the VASP code, which allows for the ab initio calculation of the thermal conductivity (lattice and electronic parts), electrical conductivity and Seebeck coefficient. Applications to several conventional thermoelectric materials will be considered, and their thermoelectric figure of merit will be computed.

FK-1:IL05  Recent Advances in Understanding of Resonant States in Thermoelectric Materials
B. Wiendlocha, Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow, Poland

In my talk I will present recent results which extend our understanding of resonant levels in thermoelectric semiconductors. First is related to the important problem of identification of a resonant impurity. A widely-used method to demonstrate the resonant behavior of a dopant relies on the construction of the Ioffe-Pisarenko plot and observation of the enhancement of the thermopower for a specific dopant. However, deviations from the Pisarenko plot may be induced by other non-resonant effects, making this method inconclusive. Here, based on the theoretical and experimental work, a novel methodology is shown which allows to conclude on the resonant character of the impurity independently from the thermopower measurements. It is based on the analysis of the residual resistivity and carrier mobility, and its usefulness is demonstrated on the examples of SnTe and PbTe [1]. Next I will show how resonant and quasi-local in-gap states helped recently to boost the thermoelectric efficiency of the double-doped n- and p-type PbTe to 15% in the temperature range between 300K and 800 K [2,3].
[1] B. Wiendlocha et al, Mater Horizons 2021, 8, 1735 [2] T. Parashchuk et al, ACS Appl Mater Interfaces, 10.1021/acsami.1c14236 [3] K. T. Wojciechowski et al, J Mater Chem C 2020, 8, 13270

FK-1:L09  Innovative Oxidation Protective Glass Coating for Magnesium Silicide-based Thermoelectrics
F. D'ISANTO¹, F. Smeacetto¹, K. Chen², M.J. Reece², M. Salvo¹. ¹Department of Applied Science and Technology (DISAT), Politecnico di Torino, Torino, Italy; ²Nanoforce Technology Limited and School of Engineering & Materials Science, Queen Mary University of London, London, UK

Magnesium silicide is considered a promising thermoelectric material to generate electricity from waste-heat thanks to its good thermoelectric performance, low-cost, low-toxicity and light-weight. Nevertheless, the stability and oxidation resistance over time at temperatures higher than 500° C are critical issues. Glass-based materials, with low electrical and thermal conductivity, are good candidates for oxidation protective coatings. In this work, a Mg2Si-Mg2Sn based thermoelectric, densified by spark plasma sintering (SPS), was successfully coated with a new silica-based glass, which was specifically designed as an oxidation protective coating for mid-temperature range (up to 500° C) applications. Despite the high coefficient of thermal expansion of Mg2(Si,Sn), very good thermo-mechanical compatibility between the substrate and the coating was obtained. Oxidation tests, performed at 500° C for 120 hrs in air, established the effectiveness of the glass coating for the protection of Sb doped Mg2(Si,Sn) thermoelectrics.

FK-1:IL10  Layered Chalcogenides as Thermoelectric Materials
P. VAQUEIRO, Department of Chemistry, University of Reading, Reading, UK

The need for alternative energy generation technologies has led to a tremendous growth of research into new thermoelectric materials. Compared with oxides, chalcogenides show a greater tendency to exhibit low-dimensional structural units, which can lead to a highly structured density of states and hence to a high thermoelectric power factor. For instance, high power factors can be achieved in layered titanium disulfide. The structure of this material consists of 2-dimensional blocks separated by a van der Waals gap. Introduction of a guest into the van der Waals gap enables tuning of the electron transport properties and hence the power factor. Exfoliation of layered chalcogenides provides opportunities for the preparation of composites, which can exhibit marked reductions in lattice thermal conductivity, through increased phonon scattering at the interfaces. The complex bonding found in pseudo-layered materials such as In4Se3, can also lead to low thermal conductivities. In In4Se3, low thermal conductivity is a consequence of rattling vibrations of weakly-bonded monovalent In cations located between strongly-bonded layers. Similarly, in BiCuOQ (Q = S, Se, Te), weak bonding of copper atoms leads to an unexpected vibrational mode at low frequencies.

FK-1:IL11  Unexpected Interstitials in Half-Heusler Compounds
WENJIE XIE1, R. Yan1, A. Weidenkaff1, 2, 1Department of Materials and Earth Sciences, Technical University of Darmstadt, Darmstadt, Germany; 2Fraunhofer Research Institution for Materials Recycling and Resource Strategies IWKSK, Germany

Half-Heusler (HH) compounds are promising thermoelectric (TE) candidates. Such ternary intermetallics with a general formula XYZ (X, Y = transition metal, Z = main group element) crystallize in a cubic MgAgAs-type structure ( , space group 216). In the crystal structure of HH, the X, Y, and Z atoms occupy the Wyckoff positions 4a (0, 0, 0), 4c (1/4, 1/4, 1/4), and 4b (1/2, 1/2, 1/2), respectively, leaving the 4d (3/4, 3/4, 3/4) sites vacant. While, when Y atoms partially occupy the Wyckoff position 4d, interstitial defects are formed in the HH structure. The interstitial defects can modify the position of the Fermi level inside the band gap and the value of the band gap, thus significantly influencing the transport properties of HH compounds. This talk will take ZrNiSn and NbCoSn as examples to show that unexpected interstitials formed in the arc-melted samples. The formation mechanism of the interstitial defects and the influence of interstitials on the transport properties of ZrNiSn and NbCoSn will be discussed.

FK-1:IL13  Thermomagnetic Transport in Layered Topological Semimetals
M. ZEBARJADI, Md.S. Akhanda, E. Rezaei, K. Esfarjani, University of Virginia, Charlottesville, VA, USA; S. Krylyuke, A.V. Davydov, N, Material Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, USA

Thermomagnetic power generators and coolers are an alternative to thermoelectric modules. They have several advantages compared to their thermoelectric counterparts such as exhibiting higher energy conversion efficiency for the same zT (adiabatic) (applicable when the zT (adiabatic) is greater than 0.2), better suitability for energy conversion in the case of thin films, and simpler design as the module can be made using only one material compared to two (n-type and p-type) in case of a thermoelectric module. The transport of electrons and phonons are decoupled as the temperature gradient and the electrical current directions are perpendicular to each other. Here we study layered semi-metallic materials for thermomagnetic applications. Layered materials have a low thermal conductivity perpendicular to the layers due to the weak van der Waals bonding between the layers. The semi-metallic nature is advantageous for building up a larger Nernst voltage due to bipolar transport and finally, the topological nature of the materials allows larger carrier mobility. In this talk, I will present our results on Bi2Te3, NbSe2, and MoTe2 samples.

FK-1:IL14  High-performance Thermoelectric Oxides
A.V. KOVALEVSKY, G. Constantinescu, D. Lopes, K.V. Zakharchuk, S. Rasekh, A.A. Yaremchenko, CICECO - Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, Aveiro, Portugal; N.M. Ferreira, i3N, Physics Department, University of Aveiro, Aveiro, Portugal; W. Xie, A. Weidenkaff, Materials and Resources, Techn. Universität Darmstadt, Darmstadt, Germany; A. Galatanu, National Institute of Materials Physics, Magurele, Romania; M.H. Aguirre, Condensed Matter Physics Department, University of Zaragoza, Institute of Material Science of Aragón, ICMA-CSIC, Zaragoza, Spain; Advanced Microscopy Laboratory I+D Building-Campus Río Ebro, Zaragoza, Spain

Oxide materials represent a promising alternative to traditional thermoelectrics, by providing a possibility to operate at high temperatures, resulting in a higher Carnot efficiency. Although their conversion efficiency is considerably lower, their known structural and microstructural versatility can open new horizons for thermoelectric applications. This work reviews some representative cases of engineering the composition and microstructure of oxides towards high thermoelectric performance. The selected approaches will include laser processing, in-situ formed composites, defects tailoring and aluminothermy-boosted sintering, also taking into account the unique redox-tuning capabilities of oxides. Representative examples will include ceramic materials based on SrTiO3, ZnO, CaMnO3 and Ca3Co4O9.

FK-1:IL17  Ultrahigh Thermoelectric Figure of Merit in Hole-doped Polycrystalline SnSe
IN CHUNG, School of Chemical and Biological Engineering, Seoul National University, Seoul, South Korea

Single-crystal SnSe was discovered to exhibit extraordinarily high thermoelectric figure of merit (ZT) ~2.2-2.6 at 913 K because of its favorable electronic structure and ultralow lattice thermal conductivity. However, more practical and deployable polycrystal form of SnSe has shown much poorer overall ZT. Accordingly, the widely sought goal in the thermoelectric society has been to realizing polycrystalline SnSe samples with comparable to or even higher performance than the single-crystals. The poor bulk thermoelectric performance of the polycrystals is attributed to the presence of traces of tin oxides forming thin film on the surface of SnSe powders, which unfavorably increases the overall thermal conductivity, decreases electrical conductivity and consequently reducing ZT below the expected level. In this talk, I will present that hole-doped SnSe polycrystalline samples with their tin oxides properly removed show a record-breaking peak ZT greater than ~3.1 at 783 K and average ZT ~2.0 between 400 and 783 K. Their lattice thermal conductivity reaches down to an ultralow level of ~0.07 W m–1K–1 at 783 K, much lower than that of the single-crystals. I will also uncover the origin of surface tin oxides and the solution to this, enabling unprecedented bulk thermoelectric performances.

FK-1:L19  Boosting the Anisotropic Thermoelectric Performance of PEDOT:PSS by Brush Printing
BOKAI ZHANG, F. Molina-Lopez, KU Leuven, Leuven, Belgium

Organic thermoelectrics (OTEs) introduces various advantages such as low production cost, large-area processing, material abundance, and flexibility. However, the broad application of OTEs is limited by their relatively low performance. Existing research of OTEs has focused on new materials exploration and doping, but not much attention has been paid to molecular ordering, a well-known strategy to improve the performance of the organic transistor. Our goal is to develop a versatile method to boost the performance of thin-film OTEs by inducing uniaxial molecular alignment via brush printing. It is expected that the directional capillarity effect produced by the brush bristles will induce PEDOT chain alignment during deposition. Applying a post-treatment by solvent-brushing will remove the excess of PSS along the selected direction too, further enhancing material anisotropy and transport. Inducing morphological anisotropy at the nanoscale can increase the electrical to thermal conductivity ratio along the aligned direction without strongly affecting the Seebeck coefficient. This will lead to the enhancement of thermoelectric properties such as the power factor, and even the figure of merit (ZT). This research provides a new solution for producing high-performance OTE materials.

FK-1:IL21  Optimization of Thermoelectric Properties in Some Transition Metal Sulfides: the Role of Magnetism
S. HEBERT, Laboratoire CRISMAT Normandie Université, UMR6508 CNRS, ENSICAEN, UNICAEN, Caen, France

In transition metal sulfides, transport and magnetic properties can be closely related due to the sensitivity of the band structure to magnetism, or due to spin dependent carriers hopping phenomena similar to the ones observed in colossal magneto-resistant oxides [1]. This interplay can also be observed on the thermoelectric transport properties, as evidenced by the large magnetoSeebeck effect observed in the thiospinel CuCrTiS4, together with a large magnetoresistance [2]. Several examples will be shown in this talk on the optimization of thermoelectric properties in some magnetic sulfides. We will discuss how the magnetism can modify the thermoelectric transport and also induce the enhancement of the Seebeck coefficient through entropic effects [3].
[1] : A. P. Ramirez et al., Nature 386, 156 (1997). [2] : D. Berthebaud, O. I. Lebedev, A. Maignan et al., J. Appl Phys. 124, 063905 (2018). [3] : Sylvie Hébert, Ramzy Daou, Antoine Maignan, Subarna Das, Aritra Banerjee, Yannick Klein, Cédric Bourgès, Naohito Tsujii & Takao Mori, STAM22, 583 (2021).

FK-1:IL24  Current Progress and Challenges in Organic Thermoelectrics
M. CAMPOY-QUILES, O. ZAPATA, Institute of Materials Science of Barcelona (ICMAB-CSIC), Bellaterra, Spain

Heat is a ubiquitous, albeit diluted, source of energy. Solid state heat-to-electricity converters, i.e. thermoelectrics, have strong potential to harvest part of this untapped diluted energy source. Solution processed carbon based materials are currently being investigated as a very promising alternative for low-cost, low temperature thermoelectrics based on abundant and non-toxic materials, which, moreover, can be easily produced in different shapes in order to wrap around curved heat sources and thus maximize heat transfer. Contrary to most inorganic semiconductors, organics often exhibit low thermal conductivities, but modest electrical conductivities, and thus a strong focus of research is devoted to increase the electronic properties leaving thermal transport unaffected [1]. In this talk I will describe the progress and challenges in organic thermoelectrics, focusing on our current understanding of what governs the main material thermoelectric properties. In addition, I will describe some recent strategies to overcome these limitations based on advanced processing schemes [2] and fabrication of composites [3].
[1] Phil. Trans. Royal Soc. A, 377, 20180352 (2019) [2] ACS Ener. Lett., 10, 1, 1902417 (2020) [3] Ener. Environ. Scie., 12, 716 (2019)

FK-1:IL25  Molybdenum-based Cluster Compounds as Candidates for High-temperature Thermoelectric Applications
C. CANDOLFI1, P. Gougeon2, P. Gall2, R. Gautier2, A. Dauscher1, B. Lenoir1, 1Institut Jean Lamour, UMR 7198 CNRS - Université de Lorraine, Nancy Cedex, France; 2Univ Rennes, CNRS, ISCR UMR 6226, INSA Rennes, ENSC Rennes, Rennes, France

Mo-based cluster compounds containing Mo6 and Mo9 cluster units have long been known for their rich chemistry and the diversity and complexity of their crystal structures. While most studies have mainly focused on their crystallographic properties, recent investigations have pointed out their potential for thermoelectric applications in power generation at high temperatures due to their good thermal stability and high melting point. Their good electrical and thermal properties are derived from the three-dimensional arrangement of the cluster units leaving large voids into which cations can reside. Their strongly-disordered character limits their ability to transport heat, leading to very low lattice thermal conductivity values on the order of 0.5 W m-1 K-1 above 300 K. In addition, most of these compounds can be driven from a metallic towards a semiconducting state through insertion of additional cations. In this communication, we will discuss the recent progress made in determining the transport properties of these compounds, presenting their key characteristics that lead to their peculiar thermal properties, and examine possible future directions to further enhance their thermoelectric performance at high temperatures.

FK-1:IL26  Si-based Nanowires for Integrated Micro Thermo-electric Generators
A. MORATA1, J.M. Sojo Gordillo1, C. Duque Sierra1, A. Tarancón1, 2, 1Catalonia Institute for Energy Research (IREC), Sant Adrià de Besòs, Barcelona, Spain; 2Institució Catalana de Recerca I Estudis Avançats (ICREA), Barcelona, Spain

Thermoelectric generators are candidates to fulfil the increased necessity of batteryless delocalized power supply in the flourishing field of the Internet of Things (IoT). So far, commercial thermoelectric devices present a number of weaknesses that have restricted their implementation to niche applications. Now it is essential to develop materials and processes with an appropriate combination of performance, cost-effectiveness and environmentally friendliness, with integrability underlying as a crucial factor simultaneously impacting these three elements. In this context, silicon-based nanostructures are promising materials for thermoelectric harvesting applications since they combine abundancy and non-toxicity with an easy integration in electronic devices, providing an enhancement of thermoelectric performance conferred by nanostructuring. We present here Si and SiGe nanowires integrated in planar silicon micromachined structures. Aligned nanowires are fabricated using a bottom-up approach that provides doped nanowires with controlled properties, epitaxially bound in selected regions of the microdevices. The performance of materials and devices is assessed, showing the feasibility of a practical implementation of this technology in integrated thermoelectric power generators.

FK-2:IL02  Thermoelectric Silicide Devices: Mechanical Reliability Large-scale Synthesis, and Module Integration
YU-CHIH TSENG, Canmet Materials, Natural Resources Canada, Hamilton, Canada

Silicide thermoelectric materials such as higher manganese silicide and magnesium silicide have gathered long-standing interest because of their low cost, low-toxicity and ease of synthesis. Although the figure-of-merit of these materials are relatively modest, they have other attributes that can enable deployment on a large scale. This presentation describes on-going work at Canmet Materials that explores the various challenges in scaling up silicide thermoelectric materials, primarily to deploy them in automotive applications. In addition to optimizing the figure-of-merit, the work at Canmet Materials examines other topics that are relevant to successful deployment. I will discuss 1) the work on understanding the mechanical properties with the aim to improve reliability, 2) possible approaches to lower the cost of synthesis and 3) integration into devices.

FK-2:IL04  Innovative Design of Thermoelectric Micro-generators based on Bismuth-telluride
S. El Oualid1, F. Kosior1, A. Dauscher1, C. Candolfi1, G. Span2, E. Mehmedovic2, J. Paris2, B. Lenoir1, 1Institut Jean Lamour, UMR 7198 CNRS, Université de Lorraine, Nancy Cedex, France; 2Mahle Thermoelektronik GmbH, Duisburg, Germany

The ever-increasing number of connected objects requires novel ways to power them and make them fully autonomous. In this context, photovoltaic, piezoelectric or thermoelectric energy-harvesting technologies show great promises as they make possible the conversion of solar radiation, motion or thermal energy into useful electricity for charging micro-batteries for instance. Thermoelectric micro-generators (μ-TEGs) exhibit several key benefits, making them prime candidates for harvesting any temperature difference between their two exchange surfaces. However, their output power critically depends on the design of the μ-TEG, the minimization of the detrimental influence of the contact resistances and on the coupling of the μ-TEG with the heat source and heat sink. Here, we theoretically and experimentally demonstrate how these inherent difficulties can be mitigated using an innovative flexible μ-TEG design based on bismuth telluride thin films. Our experimental results show that an output power of 5.5 μW per thermocouple can be generated under a temperature difference of only 5 K, in excellent agreement with predictions based on three-dimensional finite element analyses. These remarkable results rank our μ-TEG among the best micro-generators currently available.

FK-2:IL05  The Black Metal for Enhanced Thermoelectric Power Generation
CHUNLEI GUO, University of Rochester, Rochester, NY, USA

Femtosecond lasers are a powerful tool for high-precision material processing and functionalization. The femtosecond laser processing can create designer properties out of regular materials, and the laser processing led to a range of technologies developed in my lab, including the so-called black and colored metals, superhydrophillic and superhydrophobic surfaces. In this talk, I will discuss our recent developments in material engineering and particularly the applications in enhanced thermoelectric power generation.

FK-2:IL06  Phonon Engineering in Thermoelectric Materials and Flexible Thermoelectric Devices for Body Heat Harvesting and Personal Thermoregulation
WOOCHUL KIM, School of Mechanical Engineering, Yonsei University, Seoul, South Korea

In the first part of the talk, we are going to present our recent work on SnTe exhibiting zT ~ 1.9 at 929 K[1]. The main reason for such a reduction was also for the thermal conductivity reduction. The SnTe grains were coated with nanosized CdTe which is very efficient to coherently scatter phonons. In the second part, we demonstrate that conventional inorganic materials can be used in wearable systems despite their bulky and rigid nature. In particular, we proposed a bracelet-like modular design of a thermoelectric module with a heat sink integrated with Li-S battery for body heat harvesting. This continuously produces power up to 378 μW, operating a commercial glucose sensor (64 μW) and storing the remainder in the Li-S batteries[2]. For personal thermoregulation, we propose a mat-like flexible thermoelectric system based on rigid inorganic bulk materials. Using portable batteries as power sources, the refrigerated skin temperature was lowered by several degrees which are adequate for humans to perceive coldness, according to theoretical analysis. These show potential for wearable refrigeration and body heat harvesting.
Reference: [1] J. Hwang, et. al., ACS Nano 2019, 13, 8347. [2] J. Kim, et. al., Nano Energy 2020, in press.

FK-3:L02  Additive and Minimalistic Process of Flexible Inorganic Thermoelectric Devices Enabled by Laser-printing on Plastic Foil
YUAN TIAN, F. Molina-Lopez, KU Leuven, Leuven, Belgium

Thermoelectric generators (TEGs) are promising for generating electricity from the waste heat. However, the widespread use of TEGs is hindered by the expensive, hard-to-scale, complex, and limited (to simple geometries) traditional device fabrication methods. Customizing complex shapes to fit specific applications is key to optimize the device performance in real scenarios. All those needs points at additive manufacturing, especially 3D printing, as a suitable device fabrication method. In this presentation, a laser-based advanced fabrication solution is demonstrated to creatively integrate material synthesis, patterning, and assembly into a device, in one single step. Single-layer Bi2Te3-based slurries are blade-coated onto flexible substrates with tuneable thickness. By tuning the laser process parameters, N- and P-type materials are simultaneously patterned and interconnected. Thanks to the mechanical “interlock” technique developed to improve film adhesion, the untreated green material can be readily removed, leading to printed elements with relatively high shape fidelity. After encapsulation, a customized TEG device can be rapidly prototyped. This innovative fabrication method is being expanded to multi-layer printing, which will enable out-of-plane device fabrication too.

FK-3:L03  Two-in-one Management and Recovering of Thermal Energy from LTCC Flip-chip Packages
N. JAZIRI, M.-K. Iqbal, A. Schulz, H. Bartsch, J. Müller, Electronics Technology Group, Institute of Micro and Nanotechnologies MacroNano, Technische Universität Ilmenau, Ilmenau, Germany; F. Tounsi, Systems Integration & Emerging Energies (SI2E), École Nationale d'Ingénieurs de Sfax (ENIS), Université de Sfax, Sfax, Tunisia

As heat production is a main challenge for miniaturized electronics, optimizing thermal management is a central design task. However, recovering this wasted energy can be a benefit e.g. to increase independent lifetime of wireless devices. In this work, we developed a mixed thermoelectric generator (TEG) which combines lateral and vertical thermocouples to manage and harvest the wasted heat produced from a flip-chip (FC). The FC is mounted on a low temperature co-fired ceramic (LTCC) package. Since this technology is widely used as package for wireless devices, we exploit the same for harvesting. We used exclusively available LTCC compatible materials for our design. The harvester consists of multilayered lateral and vertical connected silver/silver-palladium (Ag/AgPd) thermocouples (TCs). The lateral TEG consists of 60 screen-printed Ag/AgPd thermocouples on two different layers and allows recovering the lateral heat form the FC. The second type consists of 8 TCs which also act as thermal vias to improve the FC heat transition into the heat sink. This functional improvement by the design enables the recovering of an electrical voltage VTEG=19.7 mV and an electrical power PTEG=7.4 µW at a temperature difference of ∆T=53 °C and flip chip temperature of 150 °C.

FK-3:IL05  Hybrid Thermionic-thermoelectric Generators for Concentrated Solar Radiation: Technological Advances and Future Challenges
A. BELLUCCI, Istituto di Struttura della Materia-CNR (ISM-CNR), DiaTHEMA Lab, Monterotondo (RM), Italy

Solid-state converters are very appealing devices with no moving parts, reduced maintenance, and high degree of scalability. In the sector of the solar energy conversion at high-temperature, the combination of thermionic and thermoelectric stages allows the achievement of solar-to-electric conversion efficiencies up to 41.1%. These competitive values derived mainly from the exploitation of the wasted heat released from the thermionic stage by the thermoelectric one, without any depleting effect in the performance of the two stages. First prototypes demonstrated the concept feasibility, but the efficiency was far from the calculated one. Several aspects of the technology (anti-reflective coatings, inter-electrode space, electrical connections, thermal matching, etc.) must be engineered to enhance the performance. In this presentation, the latest achieved technological improvements, and the most promising and challenging scientific solutions to develop for a further enhancement of the concept – as the use of most advanced first stage of conversion - will be described in detail for each component of the solar hybrid thermionic-thermoelectric generator. Finally, a study of integration of the proposed technology for residential small-size CSP systems will be presented.


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